How do you remove the motor oil cap, turn it which way left or right? I tried removing it but it's hard and didn't turn. I stop trying thinking i would crack it.

What motor oil velocity does my car use, 2005 C230K?

 

You won't crack it......turn counterclockwise to loosen. It's about half a turn and it will come off. Yes, they can get tight.
Here's how I do it when it's that tight.....get a pair of large channel lock type pliers and put a rag on the cap before you
use the pliers. Open them up pretty wide and hold them on the cap straight up in the air while you use your other hand to twist it off. That'll do it. Use Mobil 1 synthetic for this car. This was the factory fill, so stick with it. You can use any of the
weight oils, such as 5-30, 10-30....but there's no need for a "thicker" oil like a 20-50 for your car. I wouldn't use that one.

 

The oil cap will be hard to turn and even harder if the engine is hot, this is normal.

 

Once you add oil and replace the cap, make sure it is reinstalledproperly, sometimes it goes on what seems tight but isn't in which case it will leak. Make sure it is well installed.